An oil's usable life may vary considerably, depending on many factors, such as oil quality, engine type and condition, ambient conditions, and vehicle service schedule. Currently, automobile manufacturers recommend oil-change intervals for gasoline-engine-powered cars and light-duty trucks of either 3 months/3000 miles or 12 months/7500 miles, depending primarily on the vehicle driving cycle and ambient conditions. The use of the proper quality (i.e., SG/CD) engine oil is assumed in recommending these intervals.
Several problems exist with the current method of specifying oil-change intervals:
(1) The vehicle's Owners Manual is seldom read and is hard to understand. PA1 (2) Most drivers do not fit nearly into either of the two discrete intervals recommended. Many should probably change oil somewhere between 3 months/3000 miles and 12 months/7500 miles. PA1 (3) No provision is made for the use of the wrong quality oil. PA1 (4) No provision is made for the occurrence of engine malfunctions, such as glycol leakage, which could reduce effective oil life.
A variety of oil sensor systems are known. One system is a computer algorithm, assuming "normal" engine function and the proper quality and amount of oil in the reservoir. That system calculates effective oil life based on oil temperature histogram, which is a function of both service schedule and ambient conditions. That system overcomes the first problem by telling the driver when to change the oil, minimizing the need for understanding the recommendations in the Owner's Manual. That system also overcomes the second problem by computing oil-change intervals which are appropriate for each individual's driving schedule. However, it does not address the third or fourth problems, as it has no means of detecting oil of the wrong quality or oil overstressed due to abnormal engine operating conditions.
A device which could measure certain key physical and/or chemical characteristics of an oil in an operating engine should theoretically overcome the remaining two problems discussed above. Such a system could be used either instead of, or in conjunction with, the oil-change indicator device described above. The advantages of an oil condition sensor are that it will signal the need for an oil change when the oil's conditions warrants it; reducing the possibility for costly engine repairs due to too infrequent changes, and, conversely, eliminating the wasting of oil due to the performance of unnecessary maintenance.